In mechanical devices, such as pumps driven by a shaft connected to a motor or other means to move fluids, the shaft passes through a seal cavity, or a “stuffing box,” defined by a cylindrical cavity in the device housing. The shaft is supported by bearings at the motor end. A seal and packing rings are placed in the stuffing box to engage the shaft to prevent fluid from passing through the seal cavity and reaching the bearings and the motor, causing damage to both. It is important that appropriate packing material is placed within the seal cavity. Also, after extended use, a shaft such as a pump shaft may develop whip as the bearings wear. Thus, it is highly desirable to provide a sealing system that provides an effective seal and an additional bearing surface to reduce the whip that can occur as the shaft rotates.
In fossil fuel burning power plants and similar boilers, soot deposits collect on the heat transfer pipes, and buildup of such deposits can seriously interfere with proper heat transfer efficiency. Such power plants and boilers are provided with sootblower assemblies to clean soot from the exterior of the heat transfer pipes. Such assemblies typically include an elongate hollow tubular lance which has steam or air discharge nozzles adjacent the leading end of the tubular lance, which tubular lance is moved inward into the heat transfer chamber in generally parallel relationship to one or more adjacent heat transfer pipes to eject steam or air against these pipes to dislodge the soot therefrom. (Reference herein to steam is intended to include steam, air or any fluid used to clean the heat exchanger pipes.) The tubular lance in turn is rotatably and axially slidably supported on an elongated and cantilevered stationary steam supply pipe which projects coaxially into the tubular lance. A packing assembly cooperates between the tubular lance and a steam supply pipe to create a sealed relationship therebetween, while at the same time permitting the tubular lance to be axially and rotatably advanced into the heat exchange chamber when removal of soot is desired. Each power plant or boiler typically has a large number of such soot removal, or “sootblower”, devices. The tubular lance of each device must be cantilevered inwardly and moved a significant distance, perhaps as much as 40 feet.
Conventional sootblowers employ a plurality of packings in a seal cavity, or stuffing box, disposed axially adjacent one another for cooperation between the lance and the steam supply pipe. See, for example, U.S. Pat. Nos. 4,583,496, 5,277,153, and 6,575,122, incorporated herein by reference. These packings are able to withstand the high temperature of the steam under pressure, which is typically supplied at a temperature of about 600° F. or higher. However, inasmuch as the sootblowers are activated only periodically, such as once over an interval of several hours, the overall sootblower apparatus experiences severe differential thermal expansion characteristics when activated due to significant temperature changes when superheated steam is supplied. This makes sealing of the lance about the steam supply tube in a seal cavity or stuffing box, while still permitting relative axial and rotary movement therebetween, difficult.
While packings in sootblowers have been used with at least some success, nevertheless, packings do present disadvantages. It has been observed that use of packings in a seal cavity or stuffing box in an environment where sootblowers are used requires constant adjustment in the packing compression to achieve a proper seal while still permitting relative movement between the lance and steam supply pipe. If the packing compression is too low, then leakage occurs, and, conversely, if the compression is too high, then proper movement of the lance is difficult to achieve. Also, it has been noticed that the packings cause undesirable wear on the steam supply tube due to the significant compression required of the packing to achieve a desired seal.
Even though there are recognized disadvantages in the use of packings in sootblowers and reciprocal pumps, nevertheless, such packings have been used for many years and continue to be used in this environment in view of the lack of other satisfactory solutions. Thus, there is a need for sealing materials that provide an improved bearing surface and sealing environment for sootblowers, reciprocal pumps and other uses and that are chemically and heat resistant. Accordingly, it is desirable to provide an improved shaft seal-bearing assembly for use in the seal cavity or stuffing box of sootblowers and reciprocal pumps to provide an improved bearing surface and seal.